Future scanners will tell the difference between Advil and meth (Source: MIT)

New scanner tech uses terahertz lasers

Airport security is a huge objective in
the United States these days. Airports in America and around the
world are beefing up security and researchers scattered around the
globe are working hard at developing scanners and detectors that are
better at finding potential weapons and explosives that people may
try to get onboard aircraft.

New scanner technology that was
shown off first in May of 2009 dubbed "whole-body
imaging" scanners had passengers and privacy advocates up in
arms over the fact that the scanners were able to see through
clothing and show anatomical details of passengers. The scanners are
deployed at 40 airports at a cost of about $170,000 each. The
scanners blur the face of the person being scanned and only the
scanner operator sees the scans.

Researchers at MIT have
developed a new technology that may one day allow scanners in
airports to tell if the substance inside a medication vial is an
illegal drug or an explosive. The technology uses
lasers with a frequency in the terahertz spectrum. Lasers
operating in the terahertz range are absorbed by different molecules
in different amounts allowing scanners using the lasers to tell the
difference between chemicals.

The researchers say that
accurately determining the chemical composition of objects requires
exposing it to different and continuous ranges of terahertz
frequencies. MIT professor Qing Hu and colleagues have published a
paper in the latest issue of Nature Photonics that outlines a method
for tuning terahertz quantum cascade lasers. This is the most
promising type of laser to provide the needed terahertz radiation for
scanners. Terahertz radiation is also said to be safer for human
exposure than x-ray radiation.

Researchers discovered that
terahertz lasers could be tuned by bringing a block of another
material close to the laser beam. The blocks change the wavelength of
the laser light allowing for different frequencies. A metal block was
found to shorten the wavelength of the laser and a silicon block
lengthened it. Varying the distance of the blocks to the laser also
changed the extent of the frequency shift in the laser.

The
researchers have designed and are now building chips that use
microelectromechanical devices to bring the silicon and metal blocks
close to the laser from different directions to vary the wavelengths
from short to long. In experiments, the researchers used a mechanical
arm to move the blocks.

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